1. Field of the Invention
This invention relates to a developing device for use in an image forming apparatus such as a copying machine or a printer using a recording method of the electrophotographic type or the electrostatic recording type.
2. Description of Related Art
FIG. 9 of the accompanying drawings is a schematic cross-sectional view of a printer of the electrophotographic type.
A usually drum-shaped electrophotographic photosensitive member 150 (hereinafter referred to as the photosensitive drum 150) as a latent image bearing member is uniformly charged by a primary charger 151. Next, light is applied from an exposing device 152 onto the photosensitive drum 150 correspondingly to image information inputted from an external device to thereby form a latent image. This electrostatic latent image on the photosensitive drum 150 is made into a visible image, i.e., a toner image, by a developing device 160 by a developer T (hereinafter referred to as the toner) having the same triboelectrification polarity as the voltage applied from the primary charger 151. The toner image is transferred to a transferring material P by a transferring charger 153. The transferring material P is separated from the photosensitive drum 150 and subsequently is conveyed to a fixing device 155, and the toner image thereon is fixed thereby and thereafter becomes a permanent image. Also, any toner T not transferred by the transferring charger 153 but remaining on the photosensitive drum 150 is removed by a cleaning device 154, and the photosensitive drum 150 is used for the next image forming process.
The nonmagnetic monocomponent developing device 160 will be described here in detail with reference to FIGS. 10A and 10B of the accompanying drawings. The construction of the nonmagnetic monocomponent developing device 160 will first be shown.
In the nonmagnetic monocomponent developing device 160, generally gravity is utilized (FIG. 10A) or an agitating member is used (FIG. 10B) to carry a sufficient toner T to a developing portion having a developing roller 161 as a developer bearing member and a roller 162 (hereinafter referred to as the RS (remove and supply) roller) for supplying and removing the toner T onto and from the developing roller 161. Accordingly, the positional relationship between the developing portion and a toner containing portion becomes such that the developing portion is disposed downwardly of the toner containing portion or at a horizontal position with respect to the direction of gravity.
The toner containing portion has the toner T which is an insulative monocomponent developer and an agitating member 164. In this example, the toner T is of a negatively chargeable property and is a negatively chargeable nonmagnetic toner containing a pigment of one of yellow, magenta, cyan and black colors. As regards the agitating member 164 (FIG. 10B), a first toner agitating member 164 and a second toner agitating member 165 each comprising a plate worked into one of various shapes or a screw or the like are rotated to thereby carry the toner T in the toner containing portion to the developing roller 161. The number of the agitating members need not be two, but may be any number if they can carry the toner T from the end portion of a developing container to the vicinity of the developer bearing member 161 in accordance with one of the various constructions of the developing device 166.
In FIG. 10B, a developing container partition plate 166 is formed with a proper height so that a constant amount of toner may always be supplied onto the RS roller 162 near the developing roller 161.
In the nonmagnetic monocomponent developing method, the supply of the toner T by a magnetic force becomes impossible and therefore, the RS roller 162 made of urethane sponge is brought into contact with the developing roller 161. The RS roller 162 is rotated in a counter direction at the nip portion with the developing roller 161 to thereby supply the toner T onto the developing roller 161 and at the same time, removes the toner T on the developing roller 161 which has not been used for development even if it has passed the position opposed to the photosensitive drum 150.
A regulating blade 163 made of an elastic material such as urethane rubber as a toner amount regulating member (layer thickness regulating member) abuts against the developing roller 161 to thereby regulate the toner T on the developing roller 161 and form a thin toner layer, and prescribes the amount of toner T to be carried to a developing area (the position opposed to the photosensitive drum 150). The amount of toner T carried to the developing area is determined by the abutment pressure, the abutment length of the regulating blade 163 contacting with the developing roller 161.
The regulating blade 163 is adhesively secured or welded onto a thin metal plate of phosphor bronze, stainless!steel or the like having a thickness of several hundreds of xcexcm, and the regulating blade 163 is a chip blade made to uniformly abut against the developing roller 161 by the resiliency of the thin metal plate. At this time, the abutment condition of the regulating blade 163 is determined by the material, thickness, amount of entry and set angle of the thin metal plate.
The toner T carried to the developing area, as in the aforedescribed magnetic monocomponent developing method, adheres to the latent image on the photosensitive drum 150 to thereby visualize the latent image as a toner image.
According to the above-described monocomponent developing method, it becomes possible to form a thin toner layer suited for development by a simple construction and therefore, the downsizing and simplified maintenance of the electrophotographic apparatus are possible.
The above-described monocomponent developing device 160, however, has suffered from the problem that as image outputting is repeated for a long period of time, image density lowers and the dot reproducibility of halftone image portions lowers.
A main factor which gives rise to the above-noted problem is the deterioration of the toner T. The deterioration of the toner T refers to the aggravation of the developing characteristic such as a reduction in the chargeability of the toner T and an increase in the agglutinability of the toner T caused by an extraneous additive present on the surface of the toner T being embedded in a toner T binder.
The cause of the above-described deterioration of the toner T will be described below.
In the monocomponent developing device 160, the main cause of the deterioration of the toner T is what is called frictional contact deterioration. As described in the conventional art, in the monocomponent developing method, the photosensitive drum 150 and the developing roller 161, the developing roller 161 and the regulating blade 163, and the developing roller 161 and the RS roller 162 are brought into contact with each other with predetermined pressure with a view to output images of high quality. When the toner T passes between these, the values of physical properties including chargeability are changed by stress and frictional heat. Here, it is said that the temperature to which the toner T rises by frictional heat when it passes the developer regulating blade 163 reaches several tens of centigrade degrees or higher regarding a microscopic area called the surface of the toner T.
Also, when the circulation of the toner T in the developing device 160 is bad, the deterioration of the toner T is promoted. When the toner T once passed between the photosensitive drum 150 and the developing roller 161 and removed by the RS roller 162 is immediately supplied again to the developing roller 161 by the RS roller 162, the surface temperature of the toner T rises further by the influence of continuous stress and frictional heat and at last, it locally fuses the surface of the toner T to thereby promote the deterioration of the toner T.
As shown in the conventional art, it is popular in the construction of the conventional developing device 160 in the monocomponent developing method that the toner containing portion is upward of the developing portion constituted by the RS roller 162 and the developing roller 161 with respect to the direction of gravity, or horizontal. In these constructions, the toner T is always carried from the toner containing portion to the developing portion, which thus becomes full of the toner T. As a result, the toner T removed from the developing roller 161 exists near the RS roller 162, and exists on a toner removing path formed by the driving force of the RS roller 162 and therefore, the toner T is supplied again to the developing roller 161 before the surface of the toner T is sufficiently cooled, and as described above, the temperature of the toner T has risen and the deterioration of the toner T has occurred.
Also, in the construction of the developing device 160 shown in the conventional art, the developing portion becomes full of the toner T, whereby there also arise such problems as the blow-off of the toner T from the developing device 160, the packing phenomenon that fluidity is extremely lowered by the pressure of the weight of the toner T, and an increase in the torque of the driving of the developing roller 161 resulting from the packing phenomenon.
If conversely, the developing portion is disposed above the toner containing portion with respect to the direction of gravity, it is considered that it will not happen that as described above, the developing portion is clogged with the toner T and the circulation of the toner T becomes bad. However, in the conventional toner carrying method, it becomes very difficult to carry a necessary sufficient amount of toner T from the developer containing portion to the developing portion. It is because the toner T must be drawn up against gravity.
The present invention has been made in view of the above-noted problems and an object thereof is to provide a developing device in which it is difficult for a toner to be deteriorated.
Another object of the present invention is to provide a developing device in which it is difficult for a toner to be deteriorated and the supply of the toner to a developing roller is stable.
In one aspect, the present invention provides a developing device comprising a housing, a developer bearing member, a developer containing chamber, and a developer supplying and removing member. The developer bearing member is rotatably provided in the opening portion of the housing.
The developer supplying and removing member has the function of supplying a developer in the developer containing chamber to the developer bearing member and the function of removing the developer from the developer bearing member. The developer bearing member is disposed above the developer containing chamber, and the developer supplying and removing member has the function of upwardly carrying the developer in the developer containing chamber.
In another aspect, the present invention provides a developing device comprising a housing, a developer bearing member and a developer containing chamber. The developer bearing member is rotatably provided in the opening portion of the housing. The developer bearing member has the function of carrying the developer upwardly from within the developer containing chamber.